This is the strangest and most elusive problem we have encountered. I suspect it occurs when the Dobot attachment has recently been switched from the gripper to the suction cup. The gripper uses the air pump to both open and close, using both positive and negative air pressure. The suction cup only uses negative air pressure (or none at all).
Make sure you have specified the correct tool from the drop-down menu at the top center of DobotStudio.
If that doesn’t work, try exiting out of whatever program you’re trying to run, and create this simple Blockly program:
(Don’t add any other functionality) Run it, and the suction cup should work correctly.
I hope this article has been helpful!